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# How many prime numbers between 1 and 100 are factors of 7,15

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Math Expert
Joined: 02 Sep 2009
Posts: 65808
Re: How many prime numbers between 1 and 100 are factors of 7150  [#permalink]

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27 Jun 2018, 19:24
gmatzpractice wrote:
The tag is 600-700 level. Why is the question labeled "hard" in the Official Guide 2018 Book's Onine Question Bank?

The difficulty level of a question is calculated automatically based on the timer stats from the users which attempted the question. So our stats say that it's 600-700 level. OG says that it's hard.
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CEO
Joined: 03 Jun 2019
Posts: 3362
Location: India
GMAT 1: 690 Q50 V34
WE: Engineering (Transportation)
Re: How many prime numbers between 1 and 100 are factors of 7,15  [#permalink]

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21 Aug 2019, 01:07
seofah wrote:
How many prime numbers between 1 and 100 are factors of 7,150?

A. One
B. Two
C. Three
D. Four
E. Five

How many prime numbers between 1 and 100 are factors of 7,150?
7150 = 2*5^2*11*13

Prime factors = {2,5,11,13}

IMO D
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Kinshook Chaturvedi
Email: kinshook.chaturvedi@gmail.com
Intern
Joined: 23 Jun 2019
Posts: 5
Concentration: Finance, Organizational Behavior
How many prime numbers between 1 and 100 are factors of 7,15  [#permalink]

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21 Aug 2019, 05:32
This is how i solved it
7150/2 = 3757
3575/5 = 715 (since sum of 3575 is 20 so it is not divisible by 3)
715/5 = 143
143/11 = 13 (since 143 not divisible by 7)

So equation will be 2*5^2*11*13

I think this way you can easily solve such kind of questions.
Intern
Joined: 06 Mar 2019
Posts: 46
Schools: IMD '21
Re: How many prime numbers between 1 and 100 are factors of 7,15  [#permalink]

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22 Sep 2019, 22:25
I first simplified 7,150 to 715 x 10, then i proceeded with the prime factorization tree for 715. This made things much easier for me.
Re: How many prime numbers between 1 and 100 are factors of 7,15   [#permalink] 22 Sep 2019, 22:25

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